This invention relates to light-beam-operated heating machines, and more particularly to a light-beam-operated heating machine in which the radiation heat of a light beam is utilized to melt solder, thereby to solder, a workpiece such as an electronic component.
Examples of the above-described machines are heating machines disclosed for instance by Japanese Utility Model Application Unexamined Publication Nos. 3269/1987 and 113866/1987. One example of the arrangement of the heating machines is as shown in FIG. 7. In FIG. 7, reference numeral 1 designates an arc heat light source lamp having a point light source 2. The light source lamp is so arranged that its point light source 2 is positioned at or near the first focal point of an elliptical mirror 3. The light source lamp 1 has an anode 4 and a cathode 5 across which a supply voltage is applied by a lamp power source (not shown) to excite the point light source 2. The art heat light source lamp 1, is for instance a short arc type xenon lamp.
A thermal light beam emitted from the point light source 2 is reflected by the elliptical mirror 3. The light beam thus reflected is further reflected by a first plane mirror 6' and then by a second plane mirror 7. The angle of the first plane mirror 6 and the position of the second mirror 7 can be precisely adjusted. For instance the position of the second plane mirror 7 in a horizontal direction can be precisely adjusted by an adjusting mechanism 8. A cylindrical lens 9 is disposed in the path of the light beam reflected from the second plane mirror 7. The lens 9 is held at a predetermined angle, and its position in a horizontal direction can be precisely adjusted by an adjusting mechanism 10.
A light intercepting board 11 is provided in the path of the light beam reflected from the second plane mirror 7 and on the light incident side of the cylindrical lens 9. Each light intercepting board 11 is made up of two plates arranged along the longitudinal direction of the cylindrical lens 9. The distance between the two plates is controlled by a distance adjusting mechanism 12 so as to change the width of the light beam applied to the cylindrical lens 9.
An optical system comprising the above-described first plane mirror 6, second plane mirror 7, adjusting mechanisms 8 and 10, cylindrical lens 9 and light intercepting board 11 is provided in each of four quadrants surrounding the central axis of the elliptical mirror 3. Only two such optical systems are shown in the cross-sectional drawing, which is FIG. 1.
In the heating apparatus thus constructed the thermal light beam emitted radially from the point light source 2, being reflected by the elliptical mirror 3, forms a certain light concentrating path (a). and it is reflected in four directions by the four first plane mirrors 6 arranged in the form of a quadrangular pyramid, thus forming four optical paths (b). The light beams on the optical paths (b) are reflected by the second plane mirrors 7 to form optical paths (c). thus being applied to the cylindrical lenses 9. Each of the light beams is concentrated by the respective cylindrical lens 9 into a respective focused line of light 14 also referred to as a linear spot 14. The four linear light spots 14 are focused onto a printed circuit board 13. The linear light spots are applied near the lead wires of electronic components 15 which constitute workpieces. Since the portions of the printed circuit board which are to be irradiated by the light spots have been coated with solder in advance the solder is melted by the radiation heat of the light spots 14, whereby the lead wires are soldered to the printed circuit board.
In the light-beam-operated heating machine described above, the single light beam obtained by concentrating the output light beam of the point light source 1 with the elliptical mirror 3 is divided into four light beams with the four first plane mirrors 6 in a plane perpendicular to the optical axis of the single light beam, and the four light beams thus formed are applied to the cylindrical lenses 9 by means of the second plane mirrors 7.
FIG. 8 illustrates a front view (part A) of the conventional light concentrating optical system, a side view (part B) of the system, and a graph (part C) of the light energy distribution intensity in the longitudinal direction of the linear light spot (line of light) 14. FIG. 9 is a view across the light beam upstream of the lens 9 in the cross section A--A in FIG. 8. The line B--B in FIG. 9 represents the longitudinal direction of the linear light spot. When concentrated by lens 9 into a single line on the printed circuit board 13, the intensity varies as shown in part C of FIG. 8. In fact, the middle of the focused line of light is excessively different from that at the ends.